This is my method for filiing up the tank.

1. I fill up once a week. Every Friday on my way home from work.

--  I fill up at Kwik Trip because their 89unl is the same price as the 87unl. " Thank You KT  "

2. I use the same pump every time, each handle is uniquely sensitive as to flow output and shutoff. 

3. I set the pump handle trigger to the first autostop notch for the slowest flowrate.

4. When the pump quits, I do not pump more fuel into the tank.

5. Filling up this way should reflect fairly consistant results.